There is known a control system in which, a command value generated from a target value (target orbit) in each control cycle is provided to the feedback control system such as the servo driver, whereby the feedback control system performs feedback control such that a controlled variable that is output of a control target such as a servo motor follows the command value. Conventionally, the following two methods are known as a method for improving the following performance about the target value in the control system. First, there is a method for correcting the command value by feedforward control in which information about the command value received with the feedback control system and information about a control gain of the feedback control system are used. Second, there is a method for correcting the command value using an inverse function of a total characteristic model of the feedback control system and the control target.
For example, Japanese Patent Unexamined Application No. 2014-2474 (published on Jan. 9, 2014) discloses a method for controlling the command value provided to a servo controller (feedback control system) by feedforward control in which models of a motor (control target) and a machine system (load machine) are used.
In the first method, the command value is corrected by a simple configuration that uses feedforward control in which information about the command value received with the feedback control system and information about a control gain of the feedback control system are used, and the following performance about the target value is insufficiently improved.
In the second method, the following performance can be achieved higher than the first method when the total characteristic model of the feedback control system and the control target has good accuracy. However, in the second method, an influence of a model error of the characteristic model is directly linked to degradation of the following performance. Resultantly, in the second method, sometimes the following performance about the target value degrades in the case that the characteristic model has poor accuracy.
Accordingly, the following performance about the target value is insufficiently improved in the control system, particularly the feedback control by the conventional first and second methods.